xref: /third_party/skia/m133/src/sksl/sksl_graphite_frag.sksl

// Graphite-specific fragment shader code

const int $kTileModeClamp  = 0;
const int $kTileModeRepeat = 1;
const int $kTileModeMirror = 2;
const int $kTileModeDecal  = 3;

const int $kFilterModeNearest = 0;
const int $kFilterModeLinear  = 1;

const int $kTFTypeSRGB = 1;
const int $kTFTypePQ = 2;
const int $kTFTypeHLG = 3;
const int $kTFTypeHLGinv = 4;

const int $kColorSpaceXformFlagUnpremul = 0x1;
const int $kColorSpaceXformFlagLinearize = 0x2;
const int $kColorSpaceXformFlagGamutTransform = 0x4;
const int $kColorSpaceXformFlagEncode = 0x8;
const int $kColorSpaceXformFlagPremul = 0x10;
const int $kColorSpaceXformFlagAlphaSwizzle = 0x20;

const int $kMaskFormatA8   = 0;
const int $kMaskFormatA565 = 1;
const int $kMaskFormatARGB = 2;

const int $kShapeTypeRect = 0;
const int $kShapeTypeRRect = 1;
const int $kShapeTypeCircle = 2;

// Matches GrTextureEffect::kLinearInset, to make sure we don't touch an outer
// row or column with a weight of 0 when linear filtering.
const float $kLinearInset = 0.5 + 0.00001;

$pure half4 sk_error() {
    return half4(1.0, 0.0, 0.0, 1.0);
}

$pure half4 sk_passthrough(half4 color) {
    return color;
}

$pure half4 sk_solid_shader(float4 colorParam) {
    return half4(colorParam);
}

$pure half4 sk_rgb_opaque(float4 colorParam) {
    return half4(colorParam.rgb, 1.0);
}

$pure half4 sk_alpha_only(float4 colorParam) {
    return half4(0.0, 0.0, 0.0, colorParam.a);
}

$pure float3 $apply_xfer_fn(int kind, float3 x, half4 coeffs0, half4 coeffs1) {
    float G = coeffs0[0], A = coeffs0[1], B = coeffs0[2], C = coeffs0[3],
          D = coeffs1[0], E = coeffs1[1], F = coeffs1[2];
    float3 s = sign(x);
    x = abs(x);
    switch (kind) {
        case $kTFTypeSRGB:
            x = mix(pow(A * x + B, float3(G)) + E,
                    (C * x) + F,
                    lessThan(x, float3(D)));
            break;
        case $kTFTypePQ:
            float3 x_C = pow(x, float3(C));
            x = pow(max(A + B * x_C, 0) / (D + E * x_C), float3(F));
            break;
        case $kTFTypeHLG:
            x = mix(exp((x - E) * C) + D,
                    pow(x * A, float3(B)),
                    lessThanEqual(x * A, float3(1)));
            x *= (F + 1);
            break;
        case $kTFTypeHLGinv:
            x /= (F + 1);
            x = mix(C * log(x - D) + E,
                    A * pow(x, float3(B)),
                    lessThanEqual(x, float3(1)));
            break;
    }
    return s * x;
}

$pure half4 sk_premul_alpha(float4 color) {
    return half4(color.rgb*color.a, color.a);
}

$pure half4 sk_color_space_transform(half4 halfColor,
                                     int flags,
                                     int srcKind,
                                     half3x3 gamutTransform,
                                     int dstKind,
                                     half4x4 coeffs) {
    if (flags != 0) {
        float4 color = float4(halfColor);

        if (bool(flags & $kColorSpaceXformFlagAlphaSwizzle)) {
            color.a = dot(color.r1, float2(coeffs[1][3], coeffs[3][3]));
        }
        if (bool(flags & $kColorSpaceXformFlagUnpremul)) {
            color = unpremul(color);
        }
        if (bool(flags & $kColorSpaceXformFlagLinearize)) {
            color.rgb = $apply_xfer_fn(srcKind, color.rgb, coeffs[0], coeffs[1]);
        }
        if (bool(flags & $kColorSpaceXformFlagGamutTransform)) {
            color.rgb = gamutTransform * color.rgb;
        }
        if (bool(flags & $kColorSpaceXformFlagEncode)) {
            color.rgb = $apply_xfer_fn(dstKind, color.rgb, coeffs[2], coeffs[3]);
        }

        halfColor = bool(flags & $kColorSpaceXformFlagPremul) ? sk_premul_alpha(color)
                                                              : half4(color);
    }
    return halfColor;
}

$pure half4 sk_circular_rrect_clip(float4 rect,
                                   float2 radiusPlusHalf,
                                   half4 edgeSelect) {
    float2 fragCoord = sk_FragCoord.xy;

    // Negative x indicates inverse fill
    float2 radius = float2(abs(radiusPlusHalf.x));
    float2 dxy0 = edgeSelect.LT*((rect.LT + radius) - fragCoord);
    float2 dxy1 = edgeSelect.RB*(fragCoord - (rect.RB - radius));
    float2 dxy = max(max(dxy0, dxy1), 0.0);
    // Use more complex length calculation to manage precision issues
    half circleCornerAlpha = half(saturate(radius.x*(1.0 - length(dxy*radiusPlusHalf.y))));

    half4 rectEdgeAlphas = saturate(half4(fragCoord - rect.LT, rect.RB - fragCoord));
    rectEdgeAlphas = mix(rectEdgeAlphas, half4(1), edgeSelect);

    half alpha = circleCornerAlpha * rectEdgeAlphas.x * rectEdgeAlphas.y *
                 rectEdgeAlphas.z * rectEdgeAlphas.w;
    // Check for inverse fill
    alpha = radiusPlusHalf.x < 0 ? (1-alpha) : alpha;

    return half4(alpha);
}

$pure float $tile(int tileMode, float f, float low, float high) {
    switch (tileMode) {
        case $kTileModeClamp:
            return clamp(f, low, high);

        case $kTileModeRepeat: {
            float length = high - low;
            return (mod(f - low, length) + low);
        }
        case $kTileModeMirror: {
            float length = high - low;
            float length2 = 2 * length;
            float tmp = mod(f - low, length2);
            return (mix(tmp, length2 - tmp, step(length, tmp)) + low);
        }
        default:  // $kTileModeDecal
            // Decal is handled later.
            return f;
    }
}

$pure half4 $sample_image(float2 pos, float2 invImgSize, sampler2D s) {
    return sample(s, pos * invImgSize);
}

$pure half4 $sample_image_subset(float2 pos,
                                 float2 invImgSize,
                                 float4 subset,
                                 int tileModeX,
                                 int tileModeY,
                                 int filterMode,
                                 float2 linearFilterInset,
                                 sampler2D s) {
    // Do hard-edge shader transitions to the border color for nearest-neighbor decal tiling at the
    // subset boundaries. Snap the input coordinates to nearest neighbor before comparing to the
    // subset rect, to avoid GPU interpolation errors. See https://crbug.com/skia/10403.
    if (tileModeX == $kTileModeDecal && filterMode == $kFilterModeNearest) {
        float snappedX = floor(pos.x) + 0.5;
        if (snappedX < subset.x || snappedX > subset.z) {
            return half4(0);
        }
    }
    if (tileModeY == $kTileModeDecal && filterMode == $kFilterModeNearest) {
        float snappedY = floor(pos.y) + 0.5;
        if (snappedY < subset.y || snappedY > subset.w) {
            return half4(0);
        }
    }

    pos.x = $tile(tileModeX, pos.x, subset.x, subset.z);
    pos.y = $tile(tileModeY, pos.y, subset.y, subset.w);

    // Clamp to an inset subset to prevent sampling neighboring texels when coords fall exactly at
    // texel boundaries.
    float4 insetClamp;
    if (filterMode == $kFilterModeNearest) {
        insetClamp = float4(floor(subset.xy) + $kLinearInset, ceil(subset.zw) - $kLinearInset);
    } else {
        insetClamp = float4(subset.xy + linearFilterInset.x, subset.zw - linearFilterInset.y);
    }
    float2 clampedPos = clamp(pos, insetClamp.xy, insetClamp.zw);
    half4 color = $sample_image(clampedPos, invImgSize, s);

    if (filterMode == $kFilterModeLinear) {
        // Remember the amount the coord moved for clamping. This is used to implement shader-based
        // filtering for repeat and decal tiling.
        half2 error = half2(pos - clampedPos);
        half2 absError = abs(error);

        // Do 1 or 3 more texture reads depending on whether both x and y tiling modes are repeat
        // and whether we're near a single subset edge or a corner. Then blend the multiple reads
        // using the error values calculated above.
        bool sampleExtraX = tileModeX == $kTileModeRepeat;
        bool sampleExtraY = tileModeY == $kTileModeRepeat;
        if (sampleExtraX || sampleExtraY) {
            float extraCoordX;
            float extraCoordY;
            half4 extraColorX;
            half4 extraColorY;
            if (sampleExtraX) {
                extraCoordX = error.x > 0 ? insetClamp.x : insetClamp.z;
                extraColorX = $sample_image(float2(extraCoordX, clampedPos.y),
                                            invImgSize, s);
            }
            if (sampleExtraY) {
                extraCoordY = error.y > 0 ? insetClamp.y : insetClamp.w;
                extraColorY = $sample_image(float2(clampedPos.x, extraCoordY),
                                            invImgSize, s);
            }
            if (sampleExtraX && sampleExtraY) {
                half4 extraColorXY = $sample_image(float2(extraCoordX, extraCoordY),
                                                   invImgSize, s);
                color = mix(mix(color, extraColorX, absError.x),
                            mix(extraColorY, extraColorXY, absError.x),
                            absError.y);
            } else if (sampleExtraX) {
                color = mix(color, extraColorX, absError.x);
            } else if (sampleExtraY) {
                color = mix(color, extraColorY, absError.y);
            }
        }

        // Do soft edge shader filtering for decal tiling and linear filtering using the error
        // values calculated above.
        if (tileModeX == $kTileModeDecal) {
            color *= max(1 - absError.x, 0);
        }
        if (tileModeY == $kTileModeDecal) {
            color *= max(1 - absError.y, 0);
        }
    }

    return color;
}

$pure half4 $cubic_filter_image(float2 pos,
                                float2 invImgSize,
                                float4 subset,
                                int tileModeX,
                                int tileModeY,
                                half4x4 coeffs,
                                sampler2D s) {
    // Determine pos's fractional offset f between texel centers.
    float2 f = fract(pos - 0.5);
    // Sample 16 points at 1-pixel intervals from [p - 1.5 ... p + 1.5].
    pos -= 1.5;
    // Snap to texel centers to prevent sampling neighboring texels.
    pos = floor(pos) + 0.5;

    half4 wx = coeffs * half4(1.0, f.x, f.x * f.x, f.x * f.x * f.x);
    half4 wy = coeffs * half4(1.0, f.y, f.y * f.y, f.y * f.y * f.y);
    half4 color = half4(0);
    for (int y = 0; y < 4; ++y) {
        half4 rowColor = half4(0);
        for (int x = 0; x < 4; ++x) {
            rowColor += wx[x] * $sample_image_subset(pos + float2(x, y), invImgSize, subset,
                                                     tileModeX, tileModeY, $kFilterModeNearest,
                                                     float2($kLinearInset), s);
        }
        color += wy[y] * rowColor;
    }
    // Bicubic can send colors out of range, so clamp to get them back in gamut, assuming premul.
    color.a = saturate(color.a);
    color.rgb = clamp(color.rgb, half3(0.0), color.aaa);
    return color;
}

$pure half4 sk_image_shader(float2 coords,
                            float2 invImgSize,
                            float4 subset,
                            int tileModeX,
                            int tileModeY,
                            int filterMode,
                            sampler2D s) {
    return $sample_image_subset(coords, invImgSize, subset, tileModeX, tileModeY,
                                filterMode, float2($kLinearInset), s);
}

$pure half4 sk_cubic_image_shader(float2 coords,
                                  float2 invImgSize,
                                  float4 subset,
                                  int tileModeX,
                                  int tileModeY,
                                  half4x4 cubicCoeffs,
                                  sampler2D s) {
    return $cubic_filter_image(coords, invImgSize, subset, tileModeX, tileModeY, cubicCoeffs, s);
}

$pure half4 sk_hw_image_shader(float2 coords,
                               float2 invImgSize,
                               sampler2D s) {
    return $sample_image(coords, invImgSize, s);
}

$pure half4 $yuv_to_rgb_no_swizzle(half Y,
                                   half U,
                                   half V,
                                   half alpha,
                                   half3x3 yuvToRGBMatrix,
                                   half3 yuvToRGBTranslate) {
    half3 preColor = half3(Y, U, V);
    half4 sampleColor;
    sampleColor.rgb = saturate(yuvToRGBMatrix * preColor.rgb + yuvToRGBTranslate);
    sampleColor.a = alpha;

    // We always return an unpremul color here to skip work when transforming colorspaces
    return sampleColor;
}

$pure half4 $yuv_to_rgb(half4 sampleColorY,
                        half4 sampleColorU,
                        half4 sampleColorV,
                        half alpha,
                        half4 channelSelectY,
                        half4 channelSelectU,
                        half4 channelSelectV,
                        half3x3 yuvToRGBMatrix,
                        half3 yuvToRGBTranslate) {
    half Y = dot(channelSelectY, sampleColorY);
    half U = dot(channelSelectU, sampleColorU);
    half V = dot(channelSelectV, sampleColorV);
    return $yuv_to_rgb_no_swizzle(Y, U, V, alpha, yuvToRGBMatrix, yuvToRGBTranslate);
}

$pure half4 sk_yuv_image_shader(float2 coords,
                                float2 invImgSizeY,
                                float2 invImgSizeUV,  // Relative to Y's coordinate space
                                float4 subset,
                                float2 linearFilterUVInset,
                                int tileModeX,
                                int tileModeY,
                                int filterModeY,
                                int filterModeUV,
                                half4 channelSelectY,
                                half4 channelSelectU,
                                half4 channelSelectV,
                                half4 channelSelectA,
                                half3x3 yuvToRGBMatrix,
                                half3 yuvToRGBTranslate,
                                sampler2D sY,
                                sampler2D sU,
                                sampler2D sV,
                                sampler2D sA) {
    // If the filter modes are different between Y and UV, this means that
    // the base filtermode is nearest and we have to snap the coords to Y's
    // texel centers to get the correct positions for UV.
    if (filterModeY != filterModeUV) {
        coords = floor(coords) + 0.5;
    }

    int tileModeX_UV = tileModeX == $kTileModeDecal ? $kTileModeClamp : tileModeX;
    int tileModeY_UV = tileModeY == $kTileModeDecal ? $kTileModeClamp : tileModeY;

    half4 sampleColorY, sampleColorU, sampleColorV;
    sampleColorY = $sample_image_subset(coords, invImgSizeY, subset, tileModeX, tileModeY,
                                        filterModeY, float2($kLinearInset), sY);
    sampleColorU = $sample_image_subset(coords, invImgSizeUV, subset, tileModeX_UV, tileModeY_UV,
                                        filterModeUV, linearFilterUVInset, sU);
    sampleColorV = $sample_image_subset(coords, invImgSizeUV, subset, tileModeX_UV, tileModeY_UV,
                                        filterModeUV, linearFilterUVInset, sV);
    half alpha;
    if (channelSelectA == half4(1)) {
        alpha = 1;
    } else {
        half4 sampleColorA = $sample_image_subset(coords, invImgSizeY, subset, tileModeX, tileModeY,
                                                  filterModeY, float2($kLinearInset), sA);
        alpha = dot(channelSelectA, sampleColorA);
    }

    return $yuv_to_rgb(sampleColorY, sampleColorU, sampleColorV, alpha,
                       channelSelectY, channelSelectU, channelSelectV,
                       yuvToRGBMatrix, yuvToRGBTranslate);
}

$pure half4 sk_cubic_yuv_image_shader(float2 coords,
                                      float2 invImgSizeY,
                                      float2 invImgSizeUV,  // Relative to Y's coordinate space
                                      float4 subset,
                                      int tileModeX,
                                      int tileModeY,
                                      half4x4 cubicCoeffs,
                                      half4 channelSelectY,
                                      half4 channelSelectU,
                                      half4 channelSelectV,
                                      half4 channelSelectA,
                                      half3x3 yuvToRGBMatrix,
                                      half3 yuvToRGBTranslate,
                                      sampler2D sY,
                                      sampler2D sU,
                                      sampler2D sV,
                                      sampler2D sA) {
    int tileModeX_UV = tileModeX == $kTileModeDecal ? $kTileModeClamp : tileModeX;
    int tileModeY_UV = tileModeY == $kTileModeDecal ? $kTileModeClamp : tileModeY;

    half4 sampleColorY, sampleColorU, sampleColorV;
    sampleColorY = $cubic_filter_image(coords, invImgSizeY, subset, tileModeX, tileModeY,
                                       cubicCoeffs, sY);
    sampleColorU = $cubic_filter_image(coords, invImgSizeUV, subset, tileModeX_UV, tileModeY_UV,
                                       cubicCoeffs, sU);
    sampleColorV = $cubic_filter_image(coords, invImgSizeUV, subset, tileModeX_UV, tileModeY_UV,
                                       cubicCoeffs, sV);
    half alpha;
    if (channelSelectA == half4(1)) {
        alpha = 1;
    } else {
        half4 sampleColorA = $cubic_filter_image(coords, invImgSizeY, subset, tileModeX, tileModeY,
                                                 cubicCoeffs, sA);
        alpha = dot(channelSelectA, sampleColorA);
    }

    return $yuv_to_rgb(sampleColorY, sampleColorU, sampleColorV, alpha,
                       channelSelectY, channelSelectU, channelSelectV,
                       yuvToRGBMatrix, yuvToRGBTranslate);
}

$pure half4 sk_hw_yuv_image_shader(float2 coords,
                                   float2 invImgSizeY,
                                   float2 invImgSizeUV,  // Relative to Y's coordinate space
                                   half4 channelSelectY,
                                   half4 channelSelectU,
                                   half4 channelSelectV,
                                   half4 channelSelectA,
                                   half3x3 yuvToRGBMatrix,
                                   half3 yuvToRGBTranslate,
                                   sampler2D sY,
                                   sampler2D sU,
                                   sampler2D sV,
                                   sampler2D sA) {
    half4 sampleColorY, sampleColorU, sampleColorV, sampleColorA;
    sampleColorY = $sample_image(coords, invImgSizeY, sY);
    sampleColorU = $sample_image(coords, invImgSizeUV, sU);
    sampleColorV = $sample_image(coords, invImgSizeUV, sV);
    half alpha;
    if (channelSelectA == half4(1)) {
        alpha = 1;
    } else {
        half4 sampleColorA = $sample_image(coords, invImgSizeY, sA);
        alpha = dot(channelSelectA, sampleColorA);
    }

    return $yuv_to_rgb(sampleColorY, sampleColorU, sampleColorV, alpha,
                       channelSelectY, channelSelectU, channelSelectV,
                       yuvToRGBMatrix, yuvToRGBTranslate);
}

$pure half4 sk_hw_yuv_no_swizzle_image_shader(float2 coords,
                                              float2 invImgSizeY,
                                              float2 invImgSizeUV,  // Relative to Y's coord space
                                              half3x3 yuvToRGBMatrix,
                                              half4 yuvToRGBXlateAlphaParam,
                                              sampler2D sY,
                                              sampler2D sU,
                                              sampler2D sV,
                                              sampler2D sA) {
    half4 sampleColorY, sampleColorU, sampleColorV, sampleColorA;
    half Y = $sample_image(coords, invImgSizeY, sY).r;
    half U = $sample_image(coords, invImgSizeUV, sU).r;
    half V = $sample_image(coords, invImgSizeUV, sV).r;
    // When it's a Y_U_V_A texture, yuvToRGBXlateAlphaParam.w is 0 and we have a real A sampler so
    // alpha is just that saturated value (should be a no-op). For Y_U_V, we set
    // yuvToRGBXlateAlphaParam.w to 1 and sample from Y, which after the saturate is always 1.
    half alpha = saturate($sample_image(coords, invImgSizeY, sA).r + yuvToRGBXlateAlphaParam.w);

    return $yuv_to_rgb_no_swizzle(Y, U, V, alpha,
                                  yuvToRGBMatrix, yuvToRGBXlateAlphaParam.xyz);
}

$pure half4 sk_dither(half4 colorIn, half range, sampler2D lut) {
    const float kImgSize = 8;

    half value = sample(lut, sk_FragCoord.xy / kImgSize).r - 0.5; // undo the bias in the table
    // For each color channel, add the random offset to the channel value and then clamp
    // between 0 and alpha to keep the color premultiplied.
    return half4(clamp(colorIn.rgb + value * range, 0.0, colorIn.a), colorIn.a);
}

$pure float2 $tile_grad(int tileMode, float2 t) {
    switch (tileMode) {
        case $kTileModeClamp:
            t.x = saturate(t.x);
            break;

        case $kTileModeRepeat:
            t.x = fract(t.x);
            break;

        case $kTileModeMirror: {
            float t_1 = t.x - 1;
            t.x = t_1 - 2 * floor(t_1 * 0.5) - 1;
            if (sk_Caps.mustDoOpBetweenFloorAndAbs) {
                // At this point the expected value of tiled_t should between -1 and 1, so this
                // clamp has no effect other than to break up the floor and abs calls and make sure
                // the compiler doesn't merge them back together.
                t.x = clamp(t.x, -1, 1);
            }
            t.x = abs(t.x);
            break;
        }

        case $kTileModeDecal:
            if (t.x < 0 || t.x > 1) {
                return float2(0, -1);
            }
            break;
    }

    return t;
}

$pure half4 $colorize_grad_4(float4 colorsParam[4], float4 offsetsParam, float2 t) {
    if (t.y < 0) {
        return half4(0);

    } else if (t.x <= offsetsParam[0]) {
        return half4(colorsParam[0]);
    } else if (t.x < offsetsParam[1]) {
        return half4(mix(colorsParam[0], colorsParam[1], (t.x             - offsetsParam[0]) /
                                                         (offsetsParam[1] - offsetsParam[0])));
    } else if (t.x < offsetsParam[2]) {
        return half4(mix(colorsParam[1], colorsParam[2], (t.x             - offsetsParam[1]) /
                                                         (offsetsParam[2] - offsetsParam[1])));
    } else if (t.x < offsetsParam[3]) {
        return half4(mix(colorsParam[2], colorsParam[3], (t.x             - offsetsParam[2]) /
                                                         (offsetsParam[3] - offsetsParam[2])));
    } else {
        return half4(colorsParam[3]);
    }
}

$pure half4 $colorize_grad_8(float4 colorsParam[8], float4 offsetsParam[2], float2 t) {
    if (t.y < 0) {
        return half4(0);

    // Unrolled binary search through intervals
    // ( .. 0), (0 .. 1), (1 .. 2), (2 .. 3), (3 .. 4), (4 .. 5), (5 .. 6), (6 .. 7), (7 .. ).
    } else if (t.x < offsetsParam[1][0]) {
        if (t.x < offsetsParam[0][2]) {
            if (t.x <= offsetsParam[0][0]) {
                return half4(colorsParam[0]);
            } else if (t.x < offsetsParam[0][1]) {
                return half4(mix(colorsParam[0], colorsParam[1],
                                 (t.x                - offsetsParam[0][0]) /
                                 (offsetsParam[0][1] - offsetsParam[0][0])));
            } else {
                return half4(mix(colorsParam[1], colorsParam[2],
                                 (t.x                - offsetsParam[0][1]) /
                                 (offsetsParam[0][2] - offsetsParam[0][1])));
            }
        } else {
            if (t.x < offsetsParam[0][3]) {
                return half4(mix(colorsParam[2], colorsParam[3],
                                 (t.x                - offsetsParam[0][2]) /
                                 (offsetsParam[0][3] - offsetsParam[0][2])));
            } else {
                return half4(mix(colorsParam[3], colorsParam[4],
                                 (t.x                - offsetsParam[0][3]) /
                                 (offsetsParam[1][0] - offsetsParam[0][3])));
            }
        }
    } else {
        if (t.x < offsetsParam[1][2]) {
            if (t.x < offsetsParam[1][1]) {
                return half4(mix(colorsParam[4], colorsParam[5],
                                 (t.x                - offsetsParam[1][0]) /
                                 (offsetsParam[1][1] - offsetsParam[1][0])));
            } else {
                return half4(mix(colorsParam[5], colorsParam[6],
                                 (t.x                - offsetsParam[1][1]) /
                                 (offsetsParam[1][2] - offsetsParam[1][1])));
            }
        } else {
            if (t.x < offsetsParam[1][3]) {
                return half4(mix(colorsParam[6], colorsParam[7],
                                 (t.x                - offsetsParam[1][2]) /
                                 (offsetsParam[1][3] - offsetsParam[1][2])));
            } else {
                return half4(colorsParam[7]);
            }
        }
    }
}

$pure half4 $colorize_grad_tex(sampler2D colorsAndOffsetsSampler, int numStops, float2 t) {
    const float kColorCoord = 0.25;
    const float kOffsetCoord = 0.75;

    if (t.y < 0) {
        return half4(0);
    } else if (t.x == 0) {
        return sampleLod(colorsAndOffsetsSampler, float2(0, kColorCoord), 0);
    } else if (t.x == 1) {
        return sampleLod(colorsAndOffsetsSampler, float2(1, kColorCoord), 0);
    } else {
        float low = 0;
        float high = float(numStops);
        float invNumStops = 1.0 / high;
        for (int loop = 1; loop < numStops; loop += loop) {
            float mid = floor((low + high) * 0.5);
            float samplePos = (mid + 0.5) * invNumStops;

            float2 tmp = sampleLod(colorsAndOffsetsSampler, float2(samplePos, kOffsetCoord), 0).xy;
            float offset = ldexp(tmp.x, int(tmp.y));

            if (t.x < offset) {
                high = mid;
            } else {
                low = mid;
            }
        }

        high = (low + 1.5) * invNumStops;
        low = (low + 0.5) * invNumStops;
        half4 color0 = sampleLod(colorsAndOffsetsSampler, float2(low, kColorCoord), 0);
        half4 color1 = sampleLod(colorsAndOffsetsSampler, float2(high, kColorCoord), 0);

        float2 tmp = sampleLod(colorsAndOffsetsSampler, float2(low, kOffsetCoord), 0).xy;
        float offset0 = ldexp(tmp.x, int(tmp.y));

        tmp = sampleLod(colorsAndOffsetsSampler, float2(high, kOffsetCoord), 0).xy;
        float offset1 = ldexp(tmp.x, int(tmp.y));

        return half4(mix(color0, color1,
                         (t.x     - offset0) /
                         (offset1 - offset0)));
    }
}

$pure half4 $half4_from_array(float[] arr, int offset) {
    return half4(arr[offset + 0],
                 arr[offset + 1],
                 arr[offset + 2],
                 arr[offset + 3]);
}

$pure half4 $colorize_grad_buf(float[] colorAndOffsetData,
                               int offsetsBaseIndex,
                               int numStops,
                               float2 t) {
    int colorsBaseIndex = offsetsBaseIndex + numStops;
    if (t.y < 0) {
        return half4(0);
    } else if (t.x == 0) {
        return $half4_from_array(colorAndOffsetData, colorsBaseIndex);
    } else if (t.x == 1) {
        int lastColorIndex = colorsBaseIndex + (numStops - 1) * 4;
        return $half4_from_array(colorAndOffsetData, lastColorIndex);
    } else {
        // Binary search for the matching adjacent stop offsets running log2(numStops).
        int lowOffsetIndex = offsetsBaseIndex;
        int highOffsetIndex = lowOffsetIndex + numStops - 1;
        for (int i = 1; i < numStops; i += i) {
            int middleOffsetIndex = (lowOffsetIndex + highOffsetIndex) / 2;
            if (t.x < colorAndOffsetData[middleOffsetIndex]) {
                highOffsetIndex = middleOffsetIndex;
            } else {
                lowOffsetIndex = middleOffsetIndex;
            }
        }
        int lowColorIndex = colorsBaseIndex + (lowOffsetIndex - offsetsBaseIndex) * 4;
        float lowOffset = colorAndOffsetData[lowOffsetIndex];
        half4 lowColor = $half4_from_array(colorAndOffsetData, lowColorIndex);

        int highColorIndex = colorsBaseIndex + (highOffsetIndex - offsetsBaseIndex) * 4;
        float highOffset = colorAndOffsetData[highOffsetIndex];
        if (highOffset == lowOffset) {
            // If the t value falls exactly on a color stop, both lowOffset
            // and highOffset will be exactly the same so we avoid having
            // 0/0=NaN as our mix value.
            return lowColor;
        } else {
            half4 highColor = $half4_from_array(colorAndOffsetData, highColorIndex);

            return half4(mix(lowColor, highColor, (t.x - lowOffset) / (highOffset - lowOffset)));
        }
    }
}

$pure float2 $linear_grad_layout(float2 pos) {
    // Add small epsilon since when the gradient is horizontally or vertically aligned,
    // pixels along the same column or row can have slightly different interpolated t values
    // causing pixels to choose the wrong offset when colorizing. This helps ensure pixels
    // along the same column or row choose the same gradient offsets.
    return float2(pos.x + 0.00001, 1);
}

$pure float2 $radial_grad_layout(float2 pos) {
    float t = length(pos);
    return float2(t, 1);
}

$pure float2 $sweep_grad_layout(float biasParam, float scaleParam, float2 pos) {
    // Some devices incorrectly implement atan2(y,x) as atan(y/x). In actuality it is
    // atan2(y,x) = 2 * atan(y / (sqrt(x^2 + y^2) + x)). To work around this we pass in
    // (sqrt(x^2 + y^2) + x) as the second parameter to atan2 in these cases. We let the device
    // handle the undefined behavior if the second parameter is 0, instead of doing the divide
    // ourselves and calling atan with the quotient.
    float angle;
    if (sk_Caps.atan2ImplementedAsAtanYOverX) {
        angle = 2 * atan(-pos.y, length(pos) - pos.x);
    } else {
        // Hardcode pi/2 for the angle when x == 0, to avoid undefined behavior in this
        // case. This hasn't proven to be necessary in the atan workaround case.
        angle = pos.x != 0.0 ? atan(-pos.y, -pos.x) : sign(pos.y) * -1.5707963267949;
    }

    // 0.1591549430918 is 1/(2*pi), used since atan returns values [-pi, pi]
    float t = (angle * 0.1591549430918 + 0.5 + biasParam) * scaleParam;
    return float2(t, 1);
}

$pure float2 $conical_grad_layout(float radius0,
                                  float dRadius,
                                  float a,
                                  float invA,
                                  float2 pos) {
    // When writing uniform values, if the gradient is radial, we encode a == 0 and since
    // the linear edge case is when a == 0, we differentiate the radial case with invA == 1.
    if (a == 0 && invA == 1) {
        // Radial case
        float t = length(pos) * dRadius - radius0;

        return float2(t, 1);
    } else {
        // Focal/strip case.
        float c = dot(pos, pos) - radius0 * radius0;
        float negB = 2 * (dRadius * radius0 + pos.x);

        float t;
        if (a == 0) {
            // Linear case, both circles intersect as exactly one point
            // with the focal point sitting on that point.

            // It is highly unlikely that b and c would be 0 resulting in NaN, if b == 0 due to
            // a specific translation, it would result is +/-Inf which propogates the sign to
            // isValid resulting in how the pixel is expected to look.
            t = c / negB;
        } else {
            // Quadratic case
            float d = negB*negB - 4*a*c;
            if (d < 0) {
                return float2(0, -1);
            }

            // T should be as large as possible, so when one circle fully encloses the other,
            // the sign will be positive or negative depending on the sign of dRadius.
            // When this isn't the case and they form a cone, the sign will always be positive.
            float quadSign = sign(1 - dRadius);
            t = invA * (negB + quadSign * sqrt(d));
        }

        // Interpolated radius must be positive.
        float isValid = sign(t * dRadius + radius0);
        return float2(t, isValid);
    }
}

$pure half4 sk_linear_grad_4_shader(float2 coords,
                                    float4 colorsParam[4],
                                    float4 offsetsParam,
                                    int tileMode,
                                    int colorSpace,
                                    int doUnpremul) {
    float2 t = $linear_grad_layout(coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_4(colorsParam, offsetsParam, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_linear_grad_8_shader(float2 coords,
                                    float4 colorsParam[8],
                                    float4 offsetsParam[2],
                                    int tileMode,
                                    int colorSpace,
                                    int doUnpremul) {
    float2 t = $linear_grad_layout(coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_8(colorsParam, offsetsParam, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_linear_grad_tex_shader(float2 coords,
                                      int numStops,
                                      int tileMode,
                                      int colorSpace,
                                      int doUnpremul,
                                      sampler2D colorAndOffsetSampler) {
    float2 t = $linear_grad_layout(coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_tex(colorAndOffsetSampler, numStops, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_linear_grad_buf_shader(float2 coords,
                                      int numStops,
                                      int bufferOffset,
                                      int tileMode,
                                      int colorSpace,
                                      int doUnpremul,
                                      float[] colorAndOffsetData) {
    float2 t = $linear_grad_layout(coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_buf(colorAndOffsetData, bufferOffset, numStops, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_radial_grad_4_shader(float2 coords,
                                    float4 colorsParam[4],
                                    float4 offsetsParam,
                                    int tileMode,
                                    int colorSpace,
                                    int doUnpremul) {
    float2 t = $radial_grad_layout(coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_4(colorsParam, offsetsParam, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_radial_grad_8_shader(float2 coords,
                                    float4 colorsParam[8],
                                    float4 offsetsParam[2],
                                    int tileMode,
                                    int colorSpace,
                                    int doUnpremul) {
    float2 t = $radial_grad_layout(coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_8(colorsParam, offsetsParam, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_radial_grad_tex_shader(float2 coords,
                                      int numStops,
                                      int tileMode,
                                      int colorSpace,
                                      int doUnpremul,
                                      sampler2D colorAndOffsetSampler) {
    float2 t = $radial_grad_layout(coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_tex(colorAndOffsetSampler, numStops, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_radial_grad_buf_shader(float2 coords,
                                      int numStops,
                                      int bufferOffset,
                                      int tileMode,
                                      int colorSpace,
                                      int doUnpremul,
                                      float[] colorAndOffsetData) {
    float2 t = $radial_grad_layout(coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_buf(colorAndOffsetData, bufferOffset, numStops, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_sweep_grad_4_shader(float2 coords,
                                   float4 colorsParam[4],
                                   float4 offsetsParam,
                                   float biasParam,
                                   float scaleParam,
                                   int tileMode,
                                   int colorSpace,
                                   int doUnpremul) {
    float2 t = $sweep_grad_layout(biasParam, scaleParam, coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_4(colorsParam, offsetsParam, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_sweep_grad_8_shader(float2 coords,
                                   float4 colorsParam[8],
                                   float4 offsetsParam[2],
                                   float biasParam,
                                   float scaleParam,
                                   int tileMode,
                                   int colorSpace,
                                   int doUnpremul) {
    float2 t = $sweep_grad_layout(biasParam, scaleParam, coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_8(colorsParam, offsetsParam, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_sweep_grad_tex_shader(float2 coords,
                                     float biasParam,
                                     float scaleParam,
                                     int numStops,
                                     int tileMode,
                                     int colorSpace,
                                     int doUnpremul,
                                     sampler2D colorAndOffsetSampler) {
    float2 t = $sweep_grad_layout(biasParam, scaleParam, coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_tex(colorAndOffsetSampler, numStops, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_sweep_grad_buf_shader(float2 coords,
                                     float biasParam,
                                     float scaleParam,
                                     int numStops,
                                     int bufferOffset,
                                     int tileMode,
                                     int colorSpace,
                                     int doUnpremul,
                                     float[] colorAndOffsetData) {
    float2 t = $sweep_grad_layout(biasParam, scaleParam, coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_buf(colorAndOffsetData, bufferOffset, numStops, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_conical_grad_4_shader(float2 coords,
                                     float4 colorsParam[4],
                                     float4 offsetsParam,
                                     float radius0Param,
                                     float dRadiusParam,
                                     float aParam,
                                     float invAParam,
                                     int tileMode,
                                     int colorSpace,
                                     int doUnpremul) {
    float2 t = $conical_grad_layout(radius0Param, dRadiusParam, aParam, invAParam, coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_4(colorsParam, offsetsParam, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_conical_grad_8_shader(float2 coords,
                                     float4 colorsParam[8],
                                     float4 offsetsParam[2],
                                     float radius0Param,
                                     float dRadiusParam,
                                     float aParam,
                                     float invAParam,
                                     int tileMode,
                                     int colorSpace,
                                     int doUnpremul) {
    float2 t = $conical_grad_layout(radius0Param, dRadiusParam, aParam, invAParam, coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_8(colorsParam, offsetsParam, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_conical_grad_tex_shader(float2 coords,
                                       float radius0Param,
                                       float dRadiusParam,
                                       float aParam,
                                       float invAParam,
                                       int numStops,
                                       int tileMode,
                                       int colorSpace,
                                       int doUnpremul,
                                       sampler2D colorAndOffsetSampler) {
    float2 t = $conical_grad_layout(radius0Param, dRadiusParam, aParam, invAParam, coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_tex(colorAndOffsetSampler, numStops, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_conical_grad_buf_shader(float2 coords,
                                       float radius0Param,
                                       float dRadiusParam,
                                       float aParam,
                                       float invAParam,
                                       int numStops,
                                       int bufferOffset,
                                       int tileMode,
                                       int colorSpace,
                                       int doUnpremul,
                                       float[] colorAndOffsetData) {
    float2 t = $conical_grad_layout(radius0Param, dRadiusParam, aParam, invAParam, coords);
    t = $tile_grad(tileMode, t);
    half4 color = $colorize_grad_buf(colorAndOffsetData, bufferOffset, numStops, t);
    return $interpolated_to_rgb_unpremul(color, colorSpace, doUnpremul);
}

$pure half4 sk_matrix_colorfilter(half4 colorIn, float4x4 m, float4 v, int inHSLA, int clampRGB) {
    if (bool(inHSLA)) {
        colorIn = $rgb_to_hsl(colorIn.rgb, colorIn.a); // includes unpremul
    } else {
        colorIn = unpremul(colorIn);
    }

    half4 colorOut = half4((m * colorIn) + v);

    if (bool(inHSLA)) {
        colorOut = $hsl_to_rgb(colorOut.rgb, colorOut.a); // includes clamp and premul
    } else {
        if (bool(clampRGB)) {
            colorOut = saturate(colorOut);
        } else {
            colorOut.a = saturate(colorOut.a);
        }
        colorOut.rgb *= colorOut.a;
    }

    return colorOut;
}

// This method computes the 4 x-coodinates ([0..1]) that should be used to look
// up in the Perlin noise shader's noise table.
$pure half4 $noise_helper(half2 noiseVec,
                          half2 stitchData,
                          int stitching,
                          sampler2D permutationSampler) {
    const half kBlockSize = 256.0;

    half4 floorVal;
    floorVal.xy = floor(noiseVec);
    floorVal.zw = floorVal.xy + half2(1);

    // Adjust frequencies if we're stitching tiles
    if (bool(stitching)) {
        floorVal -= step(stitchData.xyxy, floorVal) * stitchData.xyxy;
    }

    half sampleX = sample(permutationSampler, half2((floorVal.x + 0.5) / kBlockSize, 0.5)).r;
    half sampleY = sample(permutationSampler, half2((floorVal.z + 0.5) / kBlockSize, 0.5)).r;

    half2 latticeIdx = half2(sampleX, sampleY);

    if (sk_Caps.PerlinNoiseRoundingFix) {
        // Aggressively round to the nearest exact (N / 255) floating point values.
        // This prevents rounding errors on some platforms (e.g., Tegras)
        const half kInv255 = 1.0 / 255.0;

        latticeIdx = floor(latticeIdx * half2(255.0) + half2(0.5)) * half2(kInv255);
    }

    // Get (x,y) coordinates with the permuted x
    half4 noiseXCoords = kBlockSize*latticeIdx.xyxy + floorVal.yyww;

    noiseXCoords /= half4(kBlockSize);
    return noiseXCoords;
}

$pure half4 $noise_function(half2 noiseVec,
                            half4 noiseXCoords,
                            sampler2D noiseSampler) {
    half2 fractVal = fract(noiseVec);

    // Hermite interpolation : t^2*(3 - 2*t)
    half2 noiseSmooth = smoothstep(0, 1, fractVal);

    // This is used to convert the two 16bit integers packed into rgba 8 bit input into
    // a [-1,1] vector
    const half kInv256 = 0.00390625;  // 1.0 / 256.0

    half4 result;

    for (int channel = 0; channel < 4; channel++) {

        // There are 4 lines in the noise texture, put y coords at center of each.
        half chanCoord = (half(channel) + 0.5) / 4.0;

        half4 sampleA = sample(noiseSampler, float2(noiseXCoords.x, chanCoord));
        half4 sampleB = sample(noiseSampler, float2(noiseXCoords.y, chanCoord));
        half4 sampleC = sample(noiseSampler, float2(noiseXCoords.w, chanCoord));
        half4 sampleD = sample(noiseSampler, float2(noiseXCoords.z, chanCoord));

        half2 tmpFractVal = fractVal;

        // Compute u, at offset (0,0)
        half u = dot((sampleA.ga + sampleA.rb*kInv256)*2 - 1, tmpFractVal);

        // Compute v, at offset (-1,0)
        tmpFractVal.x -= 1.0;
        half v = dot((sampleB.ga + sampleB.rb*kInv256)*2 - 1, tmpFractVal);

        // Compute 'a' as a linear interpolation of 'u' and 'v'
        half a = mix(u, v, noiseSmooth.x);

        // Compute v, at offset (-1,-1)
        tmpFractVal.y -= 1.0;
        v = dot((sampleC.ga + sampleC.rb*kInv256)*2 - 1, tmpFractVal);

        // Compute u, at offset (0,-1)
        tmpFractVal.x += 1.0;
        u = dot((sampleD.ga + sampleD.rb*kInv256)*2 - 1, tmpFractVal);

        // Compute 'b' as a linear interpolation of 'u' and 'v'
        half b = mix(u, v, noiseSmooth.x);

        // Compute the noise as a linear interpolation of 'a' and 'b'
        result[channel] = mix(a, b, noiseSmooth.y);
    }

    return result;
}

// permutationSampler is [kBlockSize x 1] A8
// noiseSampler is [kBlockSize x 4] RGBA8 premul
$pure half4 sk_perlin_noise_shader(float2 coords,
                                   float2 baseFrequency,
                                   float2 stitchDataIn,
                                   int noiseType,
                                   int numOctaves,
                                   int stitching,
                                   sampler2D permutationSampler,
                                   sampler2D noiseSampler) {
    const int kFractalNoise = 0;
    const int kTurbulence = 1;

    // In the past, Perlin noise handled coordinates a bit differently than most shaders.
    // It operated in device space, floored; it also had a one-pixel transform matrix applied to
    // both the X and Y coordinates. This is roughly equivalent to adding 0.5 to the coordinates.
    // This was originally done in order to better match preexisting golden images from WebKit.
    // Perlin noise now operates in local space, which allows rotation to work correctly. To better
    // approximate past behavior, we add 0.5 to the coordinates here. This is _not_ exactly the same
    // because this adjustment is occurring in local space, not device space.
    half2 noiseVec = half2((coords + 0.5) * baseFrequency);

    // Clear the color accumulator
    half4 color = half4(0);

    half2 stitchData = half2(stitchDataIn);

    half ratio = 1.0;

    // Loop over all octaves
    for (int octave = 0; octave < numOctaves; ++octave) {
        half4 noiseXCoords = $noise_helper(noiseVec, stitchData, stitching, permutationSampler);

        half4 tmp = $noise_function(noiseVec, noiseXCoords, noiseSampler);

        if (noiseType != kFractalNoise) {
            // For kTurbulence the result is: abs(noise[-1,1])
            tmp = abs(tmp);
        }

        color += tmp * ratio;

        noiseVec *= half2(2.0);
        ratio *= 0.5;
        stitchData *= half2(2.0);
    }

    if (noiseType == kFractalNoise) {
        // For kFractalNoise the result is: noise[-1,1] * 0.5 + 0.5
        color = color * half4(0.5) + half4(0.5);
    }

    // Clamp values
    color = saturate(color);

    // Pre-multiply the result
    return sk_premul_alpha(color);
}

$pure half4 sk_porter_duff_blend(half4 src, half4 dst, half4 coeffs) {
    return blend_porter_duff(coeffs, src, dst);
}

$pure half4 sk_hslc_blend(half4 src, half4 dst, half2 flipSat) {
    return blend_hslc(flipSat, src, dst);
}

$pure half4 sk_table_colorfilter(half4 inColor, sampler2D s) {
    half4 coords = unpremul(inColor) * (255.0/256.0) + (0.5/256.0);
    half4 color = half4(sample(s, half2(coords.r, 3.0/8.0)).r,
                        sample(s, half2(coords.g, 5.0/8.0)).r,
                        sample(s, half2(coords.b, 7.0/8.0)).r,
                        1);
    return color * sample(s, half2(coords.a, 1.0/8.0)).r;
}

$pure half4 sk_gaussian_colorfilter(half4 inColor) {
    half factor = 1 - inColor.a;
    factor = exp(-factor * factor * 4) - 0.018;
    return half4(factor);
}

$pure half4 sample_indexed_atlas(float2 textureCoords,
                                 int atlasIndex,
                                 sampler2D atlas0,
                                 sampler2D atlas1,
                                 sampler2D atlas2,
                                 sampler2D atlas3) {
    switch (atlasIndex) {
        case 1:
            return sample(atlas1, textureCoords);
        case 2:
            return sample(atlas2, textureCoords);
        case 3:
            return sample(atlas3, textureCoords);
        default:
            return sample(atlas0, textureCoords);
    }
}

$pure half3 $sample_indexed_atlas_lcd(float2 textureCoords,
                                      int atlasIndex,
                                      half2 offset,
                                      sampler2D atlas0,
                                      sampler2D atlas1,
                                      sampler2D atlas2,
                                      sampler2D atlas3) {
    half3 distance = half3(1);
    switch (atlasIndex) {
        case 1:
            distance.x = sample(atlas1, half2(textureCoords) - offset).r;
            distance.y = sample(atlas1, textureCoords).r;
            distance.z = sample(atlas1, half2(textureCoords) + offset).r;
        case 2:
            distance.x = sample(atlas2, half2(textureCoords) - offset).r;
            distance.y = sample(atlas2, textureCoords).r;
            distance.z = sample(atlas2, half2(textureCoords) + offset).r;
        case 3:
            distance.x = sample(atlas3, half2(textureCoords) - offset).r;
            distance.y = sample(atlas3, textureCoords).r;
            distance.z = sample(atlas3, half2(textureCoords) + offset).r;
        default:
            distance.x = sample(atlas0, half2(textureCoords) - offset).r;
            distance.y = sample(atlas0, textureCoords).r;
            distance.z = sample(atlas0, half2(textureCoords) + offset).r;
    }
    return distance;
}

$pure half4 bitmap_text_coverage_fn(half4 texColor, int maskFormat) {
    return (maskFormat == $kMaskFormatA8) ? texColor.rrrr
                                          : texColor;
}

$pure half4 sdf_text_coverage_fn(half texColor,
                                 half2 gammaParams,
                                 float2 unormTexCoords) {
    // TODO: To minimize the number of shaders generated this is the full affine shader.
    // For best performance it may be worth creating the uniform scale shader as well,
    // as that's the most common case.
    // TODO: Need to add 565 support.

    // The distance field is constructed as uchar8_t values, so that the zero value is at 128,
    // and the supported range of distances is [-4 * 127/128, 4].
    // Hence to convert to floats our multiplier (width of the range) is 4 * 255/128 = 7.96875
    // and zero threshold is 128/255 = 0.50196078431.
    half dist = 7.96875 * (texColor - 0.50196078431);

    // We may further adjust the distance for gamma correction.
    dist -= gammaParams.x;

    // After the distance is unpacked, we need to correct it by a factor dependent on the
    // current transformation. For general transforms, to determine the amount of correction
    // we multiply a unit vector pointing along the SDF gradient direction by the Jacobian of
    // unormTexCoords (which is the inverse transform for this fragment) and take the length of
    // the result.
    half2 dist_grad = half2(dFdx(dist), dFdy(dist));
    half dg_len2 = dot(dist_grad, dist_grad);

    // The length of the gradient may be near 0, so we need to check for that. This also
    // compensates for the Adreno, which likes to drop tiles on division by 0.
    dist_grad = (dg_len2 >= 0.0001) ? dist_grad * inversesqrt(dg_len2)
                                    : half2(0.7071);

    // Computing the Jacobian and multiplying by the gradient.
    float2x2 jacobian = float2x2(dFdx(unormTexCoords), dFdy(unormTexCoords));
    half2 grad = half2(jacobian * dist_grad);

    // This gives us a smooth step across approximately one fragment.
    half approxFragWidth = 0.65 * length(grad);

    // TODO: handle aliased rendering
    if (gammaParams.y > 0) {
        // The smoothstep falloff compensates for the non-linear sRGB response curve. If we are
        // doing gamma-correct rendering (to an sRGB or F16 buffer), then we actually want
        // distance mapped linearly to coverage, so use a linear step:
        return half4(saturate((dist + approxFragWidth) / (2.0 * approxFragWidth)));
    } else {
        return half4(smoothstep(-approxFragWidth, approxFragWidth, dist));
    }
}

$pure half4 sdf_text_lcd_coverage_fn(float2 textureCoords,
                                     half2 pixelGeometryDelta,
                                     half4 gammaParams,
                                     float2 unormTexCoords,
                                     float texIndex,
                                     sampler2D atlas0,
                                     sampler2D atlas1,
                                     sampler2D atlas2,
                                     sampler2D atlas3) {
    // TODO: To minimize the number of shaders generated this is the full affine shader.
    // For best performance it may be worth creating the uniform scale shader as well,
    // as that's the most common case.

    float2x2 jacobian = float2x2(dFdx(unormTexCoords), dFdy(unormTexCoords));
    half2 offset = half2(jacobian * pixelGeometryDelta);

    half3 distance = $sample_indexed_atlas_lcd(textureCoords,
                                               int(texIndex),
                                               offset,
                                               atlas0,
                                               atlas1,
                                               atlas2,
                                               atlas3);
    // The distance field is constructed as uchar8_t values, so that the zero value is at 128,
    // and the supported range of distances is [-4 * 127/128, 4].
    // Hence to convert to floats our multiplier (width of the range) is 4 * 255/128 = 7.96875
    // and zero threshold is 128/255 = 0.50196078431.
    half3 dist = half3(7.96875) * (distance - half3(0.50196078431));

    // We may further adjust the distance for gamma correction.
    dist -= gammaParams.xyz;

    // After the distance is unpacked, we need to correct it by a factor dependent on the
    // current transformation. For general transforms, to determine the amount of correction
    // we multiply a unit vector pointing along the SDF gradient direction by the Jacobian of
    // unormTexCoords (which is the inverse transform for this fragment) and take the length of
    // the result.
    half2 dist_grad = half2(dFdx(dist.g), dFdy(dist.g));
    half dg_len2 = dot(dist_grad, dist_grad);

    // The length of the gradient may be near 0, so we need to check for that. This also
    // compensates for the Adreno, which likes to drop tiles on division by 0.
    dist_grad = (dg_len2 >= 0.0001) ? dist_grad * inversesqrt(dg_len2)
                                    : half2(0.7071);

    // Multiplying the Jacobian by the gradient.
    half2 grad = half2(jacobian * dist_grad);

    // This gives us a smooth step across approximately one fragment.
    half3 approxFragWidth = half3(0.65 * length(grad));

    // TODO: handle aliased rendering
    if (gammaParams.w > 0) {
        // The smoothstep falloff compensates for the non-linear sRGB response curve. If we are
        // doing gamma-correct rendering (to an sRGB or F16 buffer), then we actually want
        // distance mapped linearly to coverage, so use a linear step:
        return half4(saturate((dist + approxFragWidth / (2.0 * approxFragWidth))), 1);
    } else {
        return half4(smoothstep(half3(-approxFragWidth), half3(approxFragWidth), dist), 1);
    }
}

///////////////////////////////////////////////////////////////////////////////////////////////////
// Support functions for analytic round rectangles

// Calculates 1/|∇| in device space by applying the chain rule to a local gradient vector and the
// 2x2 Jacobian describing the transform from local-to-device space. For non-perspective, this is
// equivalent to the "normal matrix", or the inverse transpose. For perspective, J should be
//    W(u,v) [m00' - m20'u  m01' - m21'u] derived from the first two columns of the 3x3 inverse.
//           [m10' - m20'v  m11' - m21'v]
$pure float $inverse_grad_len(float2 localGrad, float2x2 jacobian) {
    // NOTE: By chain rule, the local gradient is on the left side of the Jacobian matrix
    float2 devGrad = localGrad * jacobian;
    // NOTE: This uses the L2 norm, which is more accurate than the L1 norm used by fwidth().
    // TODO: Switch to L1 since it is a 2x perf improvement according to Xcode with little visual
    // impact, but start with L2 to measure the change separately from the algorithmic update.
    // return 1.0 / (abs(devGrad.x) + abs(devGrad.y));
    return inversesqrt(dot(devGrad, devGrad));
}

// Returns distance from both sides of a stroked circle or ellipse. Elliptical coverage is
// only accurate if strokeRadius = 0. A positive value represents the interior of the stroke.
$pure float2 $elliptical_distance(float2 uv, float2 radii, float strokeRadius, float2x2 jacobian) {
    // We do need to evaluate up to two circle equations: one with
    //    R = cornerRadius(r)+strokeRadius(s), and another with R = r-s.
    // This can be consolidated into a common evaluation against a circle of radius sqrt(r^2+s^2):
    //    (x/(r+/-s))^2 + (y/(r+/-s))^2 = 1
    //    x^2 + y^2 = (r+/-s)^2
    //    x^2 + y^2 = r^2 + s^2 +/- 2rs
    //    (x/sqrt(r^2+s^2))^2 + (y/sqrt(r^2+s^2)) = 1 +/- 2rs/(r^2+s^2)
    // The 2rs/(r^2+s^2) is the "width" that adjusts the implicit function to the outer or inner
    // edge of the stroke. For fills and hairlines, s = 0, which means these operations remain valid
    // for elliptical corners where radii holds the different X and Y corner radii.
    float2 invR2 = 1.0 / (radii * radii + strokeRadius*strokeRadius);
    float2 normUV = invR2 * uv;
    float invGradLength = $inverse_grad_len(normUV, jacobian);

    // Since normUV already includes 1/r^2 in the denominator, dot with just 'uv' instead.
    float f = 0.5 * invGradLength * (dot(uv, normUV) - 1.0);

    // This is 0 for fills/hairlines, which are the only types that allow
    // elliptical corners (strokeRadius == 0). For regular strokes just use X.
    float width = radii.x * strokeRadius * invR2.x * invGradLength;
    return float2(width - f, width + f);
}

// Accumulates the minimum (and negative maximum) of the outer and inner corner distances in 'dist'
// for a possibly elliptical corner with 'radii' and relative pixel location specified by
// 'cornerEdgeDist'. The corner's basis relative to the jacobian is defined in 'xyFlip'.
void $corner_distance(inout float2 dist,
                      float2x2 jacobian,
                      float2 strokeParams,
                      float2 cornerEdgeDist,
                      float2 xyFlip,
                      float2 radii) {
    float2 uv = radii - cornerEdgeDist;
    // NOTE: For mitered corners uv > 0 only if it's stroked, and in that case the
    // subsequent conditions skip calculating anything.
    if (all(greaterThan(uv, float2(0.0)))) {
        if (all(greaterThan(radii, float2(0.0))) ||
            (strokeParams.x > 0.0 && strokeParams.y < 0.0 /* round-join */)) {
            // A rounded corner so incorporate outer elliptical distance if we're within the
            // quarter circle.
            float2 d = $elliptical_distance(uv * xyFlip, radii, strokeParams.x, jacobian);
            d.y = (radii.x - strokeParams.x <= 0.0)
                      ? 1.0    // Disregard inner curve since it's collapsed into an inner miter.
                      : -d.y;  // Negate so that "min" accumulates the maximum value instead.
            dist = min(dist, d);
        } else if (strokeParams.y == 0.0 /* bevel-join */) {
            // Bevels are--by construction--interior mitered, so inner distance is based
            // purely on the edge distance calculations, but the outer distance is to a 45-degree
            // line and not the vertical/horizontal lines of the other edges.
            float bevelDist = (strokeParams.x - uv.x - uv.y) * $inverse_grad_len(xyFlip, jacobian);
            dist.x = min(dist.x, bevelDist);
        } // Else it's a miter so both inner and outer distances are unmodified
    } // Else we're not affected by the corner so leave distances unmodified
}

// Accumulates the minimum (and negative maximum) of the outer and inner corner distances into 'd',
// for all four corners of a [round] rectangle. 'edgeDists' should be ordered LTRB with positive
// distance representing the interior of the edge. 'xRadii' and 'yRadii' should hold the per-corner
// elliptical radii, ordered TL, TR, BR, BL.
void $corner_distances(inout float2 d,
                       float2x2 J,
                       float2 stroke, // {radii, joinStyle}, see StrokeStyle struct definition
                       float4 edgeDists,
                       float4 xRadii,
                       float4 yRadii) {
    $corner_distance(d, J, stroke, edgeDists.xy, float2(-1.0, -1.0), float2(xRadii[0], yRadii[0]));
    $corner_distance(d, J, stroke, edgeDists.zy, float2( 1.0, -1.0), float2(xRadii[1], yRadii[1]));
    $corner_distance(d, J, stroke, edgeDists.zw, float2( 1.0,  1.0), float2(xRadii[2], yRadii[2]));
    $corner_distance(d, J, stroke, edgeDists.xw, float2(-1.0,  1.0), float2(xRadii[3], yRadii[3]));
}

$pure half4 analytic_rrect_coverage_fn(float4 coords,
                                       float4 jacobian,
                                       float4 edgeDistances,
                                       float4 xRadii,
                                       float4 yRadii,
                                       float2 strokeParams,
                                       float2 perPixelControl) {
    if (perPixelControl.x > 0.0) {
        // A trivially solid interior pixel, either from a filled rect or round rect, or a
        // stroke with sufficiently large width that the interior completely overlaps itself.
        return half4(1.0);
    } else if (perPixelControl.y > 1.0) {
        // This represents a filled rectangle or quadrilateral, where the distances have already
        // been converted to device space. Mitered strokes cannot use this optimization because
        // their scale and bias is not uniform over the shape; Rounded shapes cannot use this
        // because they rely on the edge distances being in local space to reconstruct the
        // per-corner positions for the elliptical implicit functions.
        float2 outerDist = min(edgeDistances.xy, edgeDistances.zw);
        float c = min(outerDist.x, outerDist.y) * coords.w;
        float scale = (perPixelControl.y - 1.0) * coords.w;
        float bias = coverage_bias(scale);
        return half4(saturate(scale * (c + bias)));
    } else {
        // Compute per-pixel coverage, mixing four outer edge distances, possibly four inner
        // edge distances, and per-corner elliptical distances into a final coverage value.
        // The Jacobian needs to be multiplied by W, but coords.w stores 1/w.
        float2x2 J = float2x2(jacobian) / coords.w;

        float2 invGradLen = float2($inverse_grad_len(float2(1.0, 0.0), J),
                                   $inverse_grad_len(float2(0.0, 1.0), J));
        float2 outerDist = invGradLen * (strokeParams.x + min(edgeDistances.xy,
                                                              edgeDistances.zw));

        // d.x tracks minimum outer distance (pre scale-and-biasing to a coverage value).
        // d.y tracks negative maximum inner distance (so min() over c accumulates min and outer
        // and max inner simultaneously).)
        float2 d = float2(min(outerDist.x, outerDist.y), -1.0);
        float scale, bias;

        // Check for bidirectional coverage, which is is marked as a -1 from the vertex shader.
        // We don't just check for < 0 since extrapolated fill triangle samples can have small
        // negative values.
        if (perPixelControl.x > -0.95) {
            // A solid interior, so update scale and bias based on full width and height
            float2 dim = invGradLen * (edgeDistances.xy + edgeDistances.zw + 2*strokeParams.xx);
            scale = min(min(dim.x, dim.y), 1.0);
            bias = coverage_bias(scale);
            // Since we leave d.y = -1.0, no inner curve coverage will adjust it closer to 0,
            // so 'finalCoverage' is based solely on outer edges and curves.
        } else {
            // Bidirectional coverage, so we modify c.y to hold the negative of the maximum
            // interior coverage, and update scale and bias based on stroke width.
            float2 strokeWidth = 2.0 * strokeParams.x * invGradLen;
            float2 innerDist = strokeWidth - outerDist;

            d.y = -max(innerDist.x, innerDist.y);
            if (strokeParams.x > 0.0) {
                float narrowStroke = min(strokeWidth.x, strokeWidth.y);
                // On an axis where innerDist >= -0.5, allow strokeWidth.x/y to be preserved as-is.
                // On an axis where innerDist < -0.5, use the smaller of strokeWidth.x/y.
                float2 strokeDim = mix(float2(narrowStroke), strokeWidth,
                                       greaterThanEqual(innerDist, float2(-0.5)));
                // Preserve the wider axis from the above calculation.
                scale = saturate(max(strokeDim.x, strokeDim.y));
                bias = coverage_bias(scale);
            } else {
                // A hairline, so scale and bias should both be 1
                 scale = bias = 1.0;
            }
        }

        // Check all corners, although most pixels should only be influenced by 1.
        $corner_distances(d, J, strokeParams, edgeDistances, xRadii, yRadii);

        float outsetDist = min(perPixelControl.y, 0.0) * coords.w;
        float finalCoverage = scale * (min(d.x + outsetDist, -d.y) + bias);

        return half4(saturate(finalCoverage));
    }
}

$pure half4 per_edge_aa_quad_coverage_fn(float4 coords,
                                         float4 edgeDistances) {
    // This represents a filled rectangle or quadrilateral, where the distances have already
    // been converted to device space.
    float2 outerDist = min(edgeDistances.xy, edgeDistances.zw);
    float c = min(outerDist.x, outerDist.y) * coords.w;
    return half4(saturate(c));
}

$pure half4 circular_arc_coverage_fn(float4 circleEdge,
                                     float3 clipPlane,
                                     float3 isectPlane,
                                     float3 unionPlane,
                                     float roundCapRadius,
                                     float4 roundCapPos) {
    float d = length(circleEdge.xy);
    half distanceToOuterEdge = half(circleEdge.z * (1.0 - d));
    half edgeAlpha = saturate(distanceToOuterEdge);
    half distanceToInnerEdge = half(circleEdge.z * (d - circleEdge.w));
    half innerAlpha = saturate(distanceToInnerEdge);
    edgeAlpha *= innerAlpha;

    half clip = half(saturate(circleEdge.z * dot(circleEdge.xy, clipPlane.xy) + clipPlane.z));
    clip *= half(saturate(circleEdge.z * dot(circleEdge.xy, isectPlane.xy) + isectPlane.z));
    clip = clip + half(saturate(circleEdge.z * dot(circleEdge.xy, unionPlane.xy) + unionPlane.z));

    // We compute coverage of the round caps as circles at the butt caps produced
    // by the clip planes, and union it with the current clip.
    half dcap1 = half(circleEdge.z * (roundCapRadius - length(circleEdge.xy - roundCapPos.xy)));
    half dcap2 = half(circleEdge.z * (roundCapRadius - length(circleEdge.xy - roundCapPos.zw)));
    half capAlpha = max(dcap1, 0) + max(dcap2, 0);
    clip = saturate(clip + capAlpha);

    return half4(clip*edgeAlpha);
}

$pure half4 $rect_blur_coverage_fn(float2 coords,
                                   float4 rect,
                                   half isFast,
                                   half invSixSigma,
                                   sampler2D integral) {
    half xCoverage;
    half yCoverage;

    if (isFast != 0.0) {
        // Get the smaller of the signed distance from the frag coord to the left and right
        // edges and similar for y.
        // The integral texture goes "backwards" (from 3*sigma to -3*sigma), So, the below
        // computations align the left edge of the integral texture with the inset rect's
        // edge extending outward 6 * sigma from the inset rect.
        half2 pos = max(half2(rect.LT - coords), half2(coords - rect.RB));
        xCoverage = sample(integral, float2(invSixSigma * pos.x, 0.5)).r;
        yCoverage = sample(integral, float2(invSixSigma * pos.y, 0.5)).r;

    } else {
        // We just consider just the x direction here. In practice we compute x and y
        // separately and multiply them together.
        // We define our coord system so that the point at which we're evaluating a kernel
        // defined by the normal distribution (K) at 0. In this coord system let L be left
        // edge and R be the right edge of the rectangle.
        // We can calculate C by integrating K with the half infinite ranges outside the
        // L to R range and subtracting from 1:
        //   C = 1 - <integral of K from from -inf to  L> - <integral of K from R to inf>
        // K is symmetric about x=0 so:
        //   C = 1 - <integral of K from from -inf to  L> - <integral of K from -inf to -R>

        // The integral texture goes "backwards" (from 3*sigma to -3*sigma) which is
        // factored in to the below calculations.
        // Also, our rect uniform was pre-inset by 3 sigma from the actual rect being
        // blurred, also factored in.
        half4 rect = half4(half2(rect.LT - coords), half2(coords - rect.RB));
        xCoverage = 1 - sample(integral, float2(invSixSigma * rect.L, 0.5)).r
                      - sample(integral, float2(invSixSigma * rect.R, 0.5)).r;
        yCoverage = 1 - sample(integral, float2(invSixSigma * rect.T, 0.5)).r
                      - sample(integral, float2(invSixSigma * rect.B, 0.5)).r;
    }

    return half4(xCoverage * yCoverage);
}

$pure half4 $circle_blur_coverage_fn(float2 coords, float4 circle, sampler2D blurProfile) {
    // We just want to compute "(length(vec) - solidRadius + 0.5) / textureRadius" but need to
    // rearrange to avoid passing large values to length() that would overflow. We've precalculated
    // "1 / textureRadius" and "(solidRadius - 0.5) / textureRadius" on the CPU as circle.z and
    // circle.w, respectively.
    float invTextureRadius = circle.z;
    float normSolidRadius = circle.w;

    half2 vec = half2((coords - circle.xy) * invTextureRadius);
    float dist = length(vec) - normSolidRadius;
    return sample(blurProfile, float2(dist, 0.5)).rrrr;
}

$pure half4 $rrect_blur_coverage_fn(float2 coords,
                                    float4 proxyRect,
                                    half edgeSize,
                                    sampler2D ninePatch) {
    // Warp the fragment position to the appropriate part of the 9-patch blur texture by
    // snipping out the middle section of the proxy rect.
    float2 translatedFragPosFloat = coords - proxyRect.LT;
    float2 proxyCenter = (proxyRect.RB - proxyRect.LT) * 0.5;

    // Position the fragment so that (0, 0) marks the center of the proxy rectangle.
    // Negative coordinates are on the left/top side and positive numbers are on the
    // right/bottom.
    translatedFragPosFloat -= proxyCenter;

    // Temporarily strip off the fragment's sign. x/y are now strictly increasing as we
    // move away from the center.
    half2 fragDirection = half2(sign(translatedFragPosFloat));
    translatedFragPosFloat = abs(translatedFragPosFloat);

    // Our goal is to snip out the "middle section" of the proxy rect (everything but the
    // edge). We've repositioned our fragment position so that (0, 0) is the centerpoint
    // and x/y are always positive, so we can subtract here and interpret negative results
    // as being within the middle section.
    half2 translatedFragPosHalf = half2(translatedFragPosFloat - (proxyCenter - edgeSize));

    // Remove the middle section by clamping to zero.
    translatedFragPosHalf = max(translatedFragPosHalf, 0);

    // Reapply the fragment's sign, so that negative coordinates once again mean left/top
    // side and positive means bottom/right side.
    translatedFragPosHalf *= fragDirection;

    // Offset the fragment so that (0, 0) marks the upper-left again, instead of the center
    // point.
    translatedFragPosHalf += half2(edgeSize);

    half2 proxyDims = half2(2.0 * edgeSize);
    half2 texCoord = translatedFragPosHalf / proxyDims;

    return sample(ninePatch, texCoord).rrrr;
}

$pure half4 blur_coverage_fn(float2 coords,
                             float4 shapeData,
                             half2 blurData,
                             int shapeType,
                             sampler2D s) {
    switch (shapeType) {
        case $kShapeTypeRect: {
            return $rect_blur_coverage_fn(coords, shapeData, blurData.x, blurData.y, s);
        }
        case $kShapeTypeCircle: {
            return $circle_blur_coverage_fn(coords, shapeData, s);
        }
        case $kShapeTypeRRect: {
            return $rrect_blur_coverage_fn(coords, shapeData, blurData.x, s);
        }
    }
    return half4(0);
}